Re: [PATCH] drm/ast: Fix default resolution when no monitor is connected on DP

From: Sui Jingfeng <suijingfeng@loongson.cn>
To: Jocelyn Falempe <jfalempe@redhat.com>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	Jani Nikula <jani.nikula@linux.intel.com>,
	airlied@redhat.com, kuohsiang_chou@aspeedtech.com,
	jammy_huang@aspeedtech.com
Cc: dri-devel@lists.freedesktop.org
Subject: Re: [PATCH] drm/ast: Fix default resolution when no monitor is connected on DP
Date: Wed, 12 Jul 2023 23:05:22 +0800	[thread overview]
Message-ID: <2fb391e2-9f68-26f0-e005-a7f0f4324adc@loongson.cn> (raw)
In-Reply-To: <3fc768f8-9461-c4b0-b9af-555c52294c94@redhat.com>

Hi,

I'm here join to the discussion. Because I know a little about aspeed BMC.

On 2023/7/10 16:07, Jocelyn Falempe wrote:
> On 07/07/2023 09:30, Thomas Zimmermann wrote:
>> Hi
>>
>> Am 06.07.23 um 18:37 schrieb Jocelyn Falempe:
>> [...]
>>>>>
>>>>> You could out-comment the VGA code in the ast driver for testing.
>>>>
>>>> Oh, Thanks for the idea, I will try that.
>>>>
>>>
>>> The result is that I get a black screen on the remote BMC. So maybe 
>>> adding a remote/bmc connector will solve that.
>>
>> Could work. That would be a connector and encoder of type 'virtual'?
>>
>> Not all ast devices have a BMC. Do you know how to detect its presence?
>
> Hum, I though all ast devices have a BMC, 

No, Thomas is right, not all ast devices have a BMC.

I have two discrete AST BMC cards, see [1] for reference.

I generally using the ast2400 BMC cards to testing patches and study 
drm/ast driver.

It seems that this two cards are pure 2D display card, because they 
don't have a net interface(can not plug-in the net cable).

[1] 
https://github.com/loongson-gfx/loongson_boards/blob/main/ast_bmc_cards/ast1400_and_ast2400.jpg

> and I don't see a way to detect that BMC is active or present.

I think we better find one, then if the BMC is active (present).

we could create a virtual encoder and connector safely.

> (It would be even better to know the browser's size, and automatically 
> resize, like when using a VM. But I'm not sure the hardware/firmware 
> is able to do this).
>

I think it is not difficult, it just that need the firmware of your 
board to set a value to a register,

(a scratch register) or something like that.

But this really need you have the firmware (source code) to support this.

Or you are luckily, if there somebody already done this for you.

> On the other hand, are there any drawback to present a BMC connector 
> even when the hardware doesn't have it ?

If not properly setting up, I think you will create two encoder and two 
connector in the system.

>>
>> Best regards
>> Thomas
>>
>>>
>>>
>>
>
> Best regards,
>